Baton-wielding police stormed the two university campuses which the students had occupied. They had accused the ruling EPRDF party of fraud.
The EPRDF has won a majority of the seats declared so far.
Prime Minister Meles Zenawi banned demonstrations for a month following the poll.
"Where are they taking my son?" cried the mother of one student as he and others were herded by police onto one of eight trucks, each carrying about 80 people, reports the AP news agency.
"We are demonstrating because EPRDF is making a fraud, misleading the whole international community saying they have won," one student yelled through the gates of the social science school before the police took action.
The BBC's Mohammed Adow in Addis Ababa says tensions have been rising since the elections were held.
The opposition Coalition for Unity and Democracy (CUD) has denied government claims that it incited the students to protest.
Final election results will now be announced on 8 July - a month later than planned, the National Election Board says.
An Ethiopian policeman beating a university student using the butt of his assault rifle as another armed policeman moves in, in the capital of Addis Ababa on Monday, June 6, 2005. Police arrested hundreds of students who defied a government ban to protest the results of Ethiopia's disputed legislative elections, hours after surrounding and locking down the country's largest university on Monday.Police charged into crowds at Addis Ababa University to grab protesters and beat others in the first public protest against the May 15 elections. Army's special forces troops stood by, armed with assault rifles and rocket propelled grenades. Riot police with tear gas and a water cannon also stood by as regular police quelled the demonstration. (AP Photo/Boris Heger).